Quote Originally Posted by markis View Post
wouldnt denser colder air make more power and burn leaner as its denser so it should be more economical?
Thats not necessarily true.
Cold Air = Denser & More Volume (e.g. Oxygen).
Hot/Normal Air = Thinner & Less Volume.
The engine management system in your car will take into account the density of the air thats coming into the engine. It usually wants to keep the mixture of air and fuel at a ratio that creates complete combustion (thus more efficient, more power and also cleaner emissions).

Thus when you have a CAI, the engine management system will inject more fuel to keep this ratio and account for more oxygen coming in, giving you more power (but using more fuel).

Without a CAI, there will simply be less fuel injected to keep that same ratio.